Vestibular (balance) disorders represent a serious health problem for the American public. Although most predominant among older individuals, vestibular dysfunction can affect people of all ages. In fact, imbalance symptoms represent one of the top 25 reasons Americans seek medical care at a cost of over $1 billion per year. The consequences of vestibular disease range from vision, muscular, and mood disorders to falls and fractures. As Americans continue to lead more active lifestyles in their later years, the consequences of vestibular disease can be expected to take on added prominence. To improve our understanding of vestibular system function, we have used positional cloning strategies to identify Nox3 and Noxol, as the causative genes underlying the head tilt (het) and head slant (hslt) mouse models, respectively. These two vestibular mutants lack critical structures in the inner ear, called otoconia, that are required to detect linear acceleration and gravity. Sequence similarity of Nox3 and Noxol to known genes strongly suggests that these genes encode two members of an NADPH oxidase complex active within the vestibular system. In the proposed studies, we aim to (1) use yeast two-hybrid and computational approaches to identify other gene products within the NOX3/NOXO1 complex;(2) elucidate the role of these gene products in vestibular function by creating targeted gene knockouts in mice, and assessing their vestibular function electrophysiologically;and (3) increase our understanding of the molecular genetic pathways upstream of Nox3 using transgene analysis of predicted Nox3 regulatory elements. Together, these experiments will provide new insights into the molecular and cellular processes controlling the development, physiology, and pathology of this important vertebrate system. RELEVANCE TO PUBLIC HEALTH: The ability of healthy individuals to walk upright and maintain balance is controlled by the brain and by signals that it receives from within the inner ear's vestibular (balance) system. In the proposed experiments, the Principal Investigator aims to identify and study new genes controlling the development and function of the vestibular system. By better understanding the vestibular system, a foundation will be established to develop better treatments for such conditions as vertigo and dizziness in the hope of preventing falls and fractures.